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- using System;
- using System.Collections.Generic;
- using System.Linq;
- using System.Threading.Tasks;
- namespace System.Linq
- {
- public static partial class EnumerableEx
- {
- /// <summary>
- /// Returns elements with a distinct key value by using the default equality comparer to compare key values.
- /// </summary>
- /// <typeparam name="TSource">Source sequence element type.</typeparam>
- /// <typeparam name="TKey">Key type.</typeparam>
- /// <param name="source">Source sequence.</param>
- /// <param name="keySelector">Key selector.</param>
- /// <returns>Sequence that contains the elements from the source sequence with distinct key values.</returns>
- public static IEnumerable<TSource> Distinct<TSource, TKey>(this IEnumerable<TSource> source, Func<TSource, TKey> keySelector)
- {
- if (source == null)
- throw new ArgumentNullException(nameof(source));
- if (keySelector == null)
- throw new ArgumentNullException(nameof(keySelector));
- return source.Distinct_(keySelector, EqualityComparer<TKey>.Default);
- }
- /// <summary>
- /// Returns elements with a distinct key value by using the specified equality comparer to compare key values.
- /// </summary>
- /// <typeparam name="TSource">Source sequence element type.</typeparam>
- /// <typeparam name="TKey">Key type.</typeparam>
- /// <param name="source">Source sequence.</param>
- /// <param name="keySelector">Key selector.</param>
- /// <param name="comparer">Comparer used to compare key values.</param>
- /// <returns>Sequence that contains the elements from the source sequence with distinct key values.</returns>
- public static IEnumerable<TSource> Distinct<TSource, TKey>(this IEnumerable<TSource> source, Func<TSource, TKey> keySelector, IEqualityComparer<TKey> comparer)
- {
- if (source == null)
- throw new ArgumentNullException(nameof(source));
- if (keySelector == null)
- throw new ArgumentNullException(nameof(keySelector));
- if (comparer == null)
- throw new ArgumentNullException(nameof(comparer));
- return source.Distinct_(keySelector, comparer);
- }
- private static IEnumerable<TSource> Distinct_<TSource, TKey>(this IEnumerable<TSource> source, Func<TSource, TKey> keySelector, IEqualityComparer<TKey> comparer)
- {
- var set = new HashSet<TKey>(comparer);
- foreach (var item in source)
- {
- var key = keySelector(item);
- if (set.Add(key))
- yield return item;
- }
- }
- /// <summary>
- /// Returns consecutive distinct elements by using the default equality comparer to compare values.
- /// </summary>
- /// <typeparam name="TSource">Source sequence element type.</typeparam>
- /// <param name="source">Source sequence.</param>
- /// <returns>Sequence without adjacent non-distinct elements.</returns>
- public static IEnumerable<TSource> DistinctUntilChanged<TSource>(this IEnumerable<TSource> source)
- {
- if (source == null)
- throw new ArgumentNullException(nameof(source));
- return source.DistinctUntilChanged_(x => x, EqualityComparer<TSource>.Default);
- }
- /// <summary>
- /// Returns consecutive distinct elements by using the specified equality comparer to compare values.
- /// </summary>
- /// <typeparam name="TSource">Source sequence element type.</typeparam>
- /// <param name="source">Source sequence.</param>
- /// <param name="comparer">Comparer used to compare values.</param>
- /// <returns>Sequence without adjacent non-distinct elements.</returns>
- public static IEnumerable<TSource> DistinctUntilChanged<TSource>(this IEnumerable<TSource> source, IEqualityComparer<TSource> comparer)
- {
- if (source == null)
- throw new ArgumentNullException(nameof(source));
- if (comparer == null)
- throw new ArgumentNullException(nameof(comparer));
- return source.DistinctUntilChanged_(x => x, comparer);
- }
- /// <summary>
- /// Returns consecutive distinct elements based on a key value by using the specified equality comparer to compare key values.
- /// </summary>
- /// <typeparam name="TSource">Source sequence element type.</typeparam>
- /// <typeparam name="TKey">Key type.</typeparam>
- /// <param name="source">Source sequence.</param>
- /// <param name="keySelector">Key selector.</param>
- /// <returns>Sequence without adjacent non-distinct elements.</returns>
- public static IEnumerable<TSource> DistinctUntilChanged<TSource, TKey>(this IEnumerable<TSource> source, Func<TSource, TKey> keySelector)
- {
- if (source == null)
- throw new ArgumentNullException(nameof(source));
- if (keySelector == null)
- throw new ArgumentNullException(nameof(keySelector));
- return source.DistinctUntilChanged_(keySelector, EqualityComparer<TKey>.Default);
- }
- /// <summary>
- /// Returns consecutive distinct elements based on a key value by using the specified equality comparer to compare key values.
- /// </summary>
- /// <typeparam name="TSource">Source sequence element type.</typeparam>
- /// <typeparam name="TKey">Key type.</typeparam>
- /// <param name="source">Source sequence.</param>
- /// <param name="keySelector">Key selector.</param>
- /// <param name="comparer">Comparer used to compare key values.</param>
- /// <returns>Sequence without adjacent non-distinct elements.</returns>
- public static IEnumerable<TSource> DistinctUntilChanged<TSource, TKey>(this IEnumerable<TSource> source, Func<TSource, TKey> keySelector, IEqualityComparer<TKey> comparer)
- {
- if (source == null)
- throw new ArgumentNullException(nameof(source));
- if (keySelector == null)
- throw new ArgumentNullException(nameof(keySelector));
- if (comparer == null)
- throw new ArgumentNullException(nameof(comparer));
- return source.DistinctUntilChanged_(keySelector, comparer);
- }
- private static IEnumerable<TSource> DistinctUntilChanged_<TSource, TKey>(this IEnumerable<TSource> source, Func<TSource, TKey> keySelector, IEqualityComparer<TKey> comparer)
- {
- var currentKey = default(TKey);
- var hasCurrentKey = false;
- foreach (var item in source)
- {
- var key = keySelector(item);
- var comparerEquals = false;
- if (hasCurrentKey)
- {
- comparerEquals = comparer.Equals(currentKey, key);
- }
- if (!hasCurrentKey || !comparerEquals)
- {
- hasCurrentKey = true;
- currentKey = key;
- yield return item;
- }
- }
- }
- }
- }
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